Hydrocracking process startup



March 7, 1967 J. H. DUIR ETAL 3,308,054

HYDHOCRACKING PROCESS STARTUP Filed April e, 1964 BY /lamw .5. @5MMUnited States Patent O 3,308,054 HYDROCRACKING PROCESS STARTUP John H.Duir, Fullerton, and Arnold E. Kelley, Orange, Calif., assignors toUnion Oil Company of California, Los Angeles, Calif., a corporation ofCalifornia Filed Apr. 6, 1964, Ser. No. 357,445 9 Claims. (Cl. 208-89)This invention relates to the catalytic hydrocracking of high-boilinghydrocarbon feedstocks to produce therefrom lower boiling hydrocarbons,and more particularly is concerned with methods for initiating suchhydrocracking processes starting with a fresh, or freshly regenerated,catalyst. More specifically, the invention is concerned with theintegral hydroning-hydrocracking train, wherein a nitrogen-containingfeedstock is first subjected to catalytic hydrofining to decomposeorganic nitrogen compounds, and total effluent therefrom is thensubjected to catalytic hydrocracking (in the presence of the ammoniaformed during the hydroning operation). The basic object of theinvention is to bring the hydrocracking catalyst onstream at operativeconversion temperatures while avoiding any initial poisoning of thecatalyst resulting from contact with the organic nitrogen compounds inthe feed, and at the same time `avoiding any shock damage to thecatalyst resulting from an initial high-temperature contacting ofhydrocarbon feeds therewith.

In broad aspect, the startup procedure consists in gradually heatingboth the hydrofining and hydrocracking catalyst beds up to the desiredreaction temperatures by circulating through lboth beds in series -apreheated mixture of hydrogen and a startup feedstock which issubstantially free of organic nitrogen, while adding ammonia to saidfeedstock in such manner so as to exert a temporary poisoning effectupon the hydrocracking catalyst. Upon reaching operative hydroning andhydrocracking temperatures, the desired nitrogen-containing processfeedstock is substituted for the startup feed. By operating in thismanner, both the hydrofinin'g zone and the hydrocracking zone can bemaintained onstream in series throughout the startup procedure, and dueto the safety factor -of the added ammonia, little or no temperaturecontrol is required of the hydrofiner effluent which goes to thehydrocracker. Such a system is well adapted for use in a singleintegrated unit wherein both the hydrofining catalyst and thehydrocracking catalyst are Ilocated in the same reactor.

In the catalytic conve-rsion of hydrocarbons, the initial contacting ofthe feedstock with the fresh, or freshly regenerated, catalyst can havea profound effect upon the subsequent activity of the catalystthroughout the run. If adequate precautions are not exercised during thefirst few hours or even minutes Iof contacting, an entire batch ofcatalyst may be ruined, or explosive runaway reactions may be initiatedwhich are substantially uncontrollable. The fresh, or wil activity ofthe catalyst must be gradually tempered to the feedstock and processconditions in such manner as to avoid runaway reactions and/or undulyrapid coking rates. At the same time, precautions must be taken to-avoid poisoning by impurities which may be present in the feedstock.These problems are particularly aggravated in the case of the integralhydrofining-hydrocracking contacting train wherein the feedstockcontains organic nitrogen compounds. The basic problem involves how toget the hydroning catalyst heated to the operative hydroningtemperatures (so that substantially 'all of the organic nitrogen'compounds will be decomposed to ammonia) before the hydrofiner effluentcont-acts the hydrocracking catalyst. It has been found that amm-oniaexerts a readily reversible poisoning effect upon the hydrocrackingcatalyst, whereas ICC the -organic nitrogen compounds in the feed bringabout a relatively permanent deactivation which is reversible only byoxidative regeneration, or by very high temperature stripping.

One obvious answer to the above problem would appear to reside in simplyheating the hydrofining catalyst bed `and the hydrocracking catalystIbed separately, in parallel. This solution is not feasible in caseswhere both catalysts are enclosed in the same reactor, and moreover isundesirable even when the catalysts are enclosed in separate reactorsbecause of the added equipment required, and the unreli-ability ofcertain of the necess-ary valving arrangements in hot feed lines.

A second apparently feasible lsolution would be simply to circulateheated hydrogen, or an inert gas, serially through the hydrofningcatalyst and then through the hydrocracking catalyst until both beds areheated to the desired reaction temperature, after which the flow ofhydrocarbon feed is started. This is not practical however because it isundesirable to contact hydrocarbon feedstock initially with the catalystat the desired conversion temperaure. It is much safer, and lessdamaging to the catalyst, if the feedstock contacts the catalyst firstat relatively low temperatures, considerably below the ultimatelydesired conversion temperature, in order to precondition the catalystand temper its initial high activity.

In a copending application, Serial No. 265,648, led March 18, 1963, nowU.S. Patent No. 3,186,936, it has been proposed to solve these problemsby circulating a preheated nitrogen-free startup feedstock in seriesthrough the hydroner and the hydrocracker until the hydrofining catalystis heated to the desired conversion temperature of, c g., 700 F., andduring this heatup period, avoiding a runaway reaction in thehydrocracking catalyst bed by cooling the hydrofiner eflluent to around400 F. before i-t enters the hydrocracker. (It is imperative to avoidany contact of nitrogen-free feed mixtures with the fresh hydrocrackingcatalyst at temperatures -above about 400- 450 F.; otherwise `a runawayexothermic reaction may result.) After the hydrofining catalyst reachesthe desired conversion temperature, the nitrogen-containing process feedis then substituted for the startup feed, and after this point thehydrocracking catalyst bed can be raised to reaction temperature safelyand gradually by means of the ammonia-containing hydrofiner effluent.This procedure is feasible, but is disadvantageous from a safetystandpoint in that, during the initial heatup with nitrogen-freefeedstock, a failure in the interstage hydrofiner effluent coolingfacilities, e.g., a power failure, could result in a runaway reaction inthe hydrocracker before the system could be depressured or otherwisebrought under control. The process of this invention avoids this danger,as well as the other difficulties above discussed.

In addition to its operational advantages over the process described inSerial No. 265,648, the startup procedure of this invention is alsofound to yield in most cases a catalyst of higher initial activity thanthe process of Serial No. 265,648. This is presumably due to the morecornplete protection against organic nitrogen compounds which isafforded by the present process, but may also be due to in some measureto a specific desirable effect of ammonia on the hydrocracking catalystat low temperatures.

The poisoning effect of organic nitrogen compounds upon hydrocrackingcatalyst is well-recognized in the art. It is known that the effect canbe minimized by operating at relatively high hydrocracking temperatures,which favor desorption of nitrogen compounds. However this solution tothe problem is not practical because high hydrocracking temperaturesgive relatively nonselective cracking, with much production of lightgases and coke. We

have found however that at relatively low hydrocracking temperatures,below about 825 F., there is a marked difference between the poisoningeffect of organic nitrogen compounds or at least some types thereof), ascompared to ammonia. With a sufliciently active catalyst, substantialamounts of ammonia can be tolerated in the reaction zone, whereasorganic nitrogen compounds are much more detrimental. Specifically, ithas been found that organic nitrogen compounds tend to becomeirreversibly adsorbed on the catalyst, and exert a relatively permanentpoisoning effect at the low hydrocracking temperatures employed herein.As a result of this phenomenon, if the hydrocracking catalyst is broughtup to hydrocracking temperatures, as, e.g., from room temperature, bymeans of preheated feed-hydrogen mixtures containing organic nitrogencompounds, a much lower activity is obtained than if the feed werepretreated to decompose the organic nitrogen compounds into ammonia.Moreover, this low activity level persists for at least several weeks,and normally cannot be reversed except by going to hydrocrackingtemperatures above about 825 F., at which the catalyst is damaged bycoke laydown.

From the foregoing, it will be apparent that the principal objective ofthe invention is to provide economical methods for the hydrocracking ofnitrogen-containing feedstocks at relatively low temperatures, belowabout 800 F. A further object is to provide methods for hydrocrackingnitrogen-containing feedstocks which avoid the conventional andexpensive non-integral prehydroning of such feedstocks with itsconcomitant interstage condensation and washing to remove ammoniatherefrom. A specific objective is to provide, in an integralhydrofininghydrocracking sequence, a convenient and economical methodfor raising the hydroning and hydrocracking catalyst to the desiredoperating temperatures without damaging the hydrocracking catalysts.Other objectives will be apparent from the more detailed descriptionwhich follows.

Reference is now made to the accompanying drawings wherein FIGURE 1 is aowsheet illustrating a preferred startup procedure of the invention, andFIGURE 2 is a graph depicting a specific illustrative startup schedule(carried out at 1,500 p.s.i.g., a feed rate of 1.0 LHSV in thehydrofiner, and 1.5 LHSV in the hydrocracker) wherein feed composition,ammonia addition, and reactor inlet temperatures are correlated withtime. The flow diagram of FIGURE 1 will be explained with specicreference to the startup schedule -of FIGURE 2.

In FIGURE l, hydroner 2 is operated adiabatically, but if desired, amore isothermal operation may be obtained by means of one or moreintermediate quench points, as in hydrocracker 4. Hydrocracker 4 issemiadiabatic in that two hydrogen quench points are utilized betweenhydrocracking catalyst beds 6, 8 and 10. At the beginning of theoperation to be described, hydroning catalyst bed 12 and hydrocrackingcatalyst beds 6, 8 and 10 have been yfreshly activated and brought to atemperature of about 300 F. by means of a circulating recycle hydrogenstream. The hydroning catalyst is also preferably in a presuldedcondition.

The process utilizes a low-nitrogen startup feed, and a high-nitrogenprocess feed. The startup feed should contain less than about 100 parts,and preferably less than about 10 parts per million of organic nitrogen;the process feed contains relatively more nitrogen, up to about 2% byweight or more. Either or both of the feedstocks may contain sulfur inamounts up to about by weight, although it is preferable to use astartup feed which contains less than about 1% of sulfur. In otherrespects the feeds may if desired be similar in character, although itis further preferred that the startup feed contain less than about 35%by volume of aromatic hydrocarbons in order to minimize exothermictemperature rises in hydrocracker 4. Preferred characteristics of therespective feedstocks are as follows:

To initiate the startup procedure, valve 14 in low-nitrogen startup feedline 16 is opened, as well as valve 18 in ammonia injection line 20,while valve 22 in high-nitrogen feed line 24 is closed. The startup feedplus ammonia (preferably anhydrous liquid ammonia) thus flows from lines16 and 20 respectively into reactor feed line 26 wherein it is mixedwith hydrogen from line 28. The hydrogen used during the startupsequence is preferably sour, containing, e.g., from 0.1-1% by volume ofhydrogen sulfide, in order to maintain the hydrofining catalyst in asulfided condition, and to effect a gradual sulding of the hydrocrackingcatalyst. The ratio of hydrogen to feed in line 26 is preferably betweenabout 1,000 and 20,000 s.c.f./b. The startup feed iiow rates may besubstantially in the range of the flow rates hereinafter specified forthe high-nitrogen process feeds, and the respective pressures may alsobe in the same range. Preferred ammonia concentrations during startuprange between about 0.1 yand 1% by weight of the startup feed. Theammonia may be added in the form of gaseous or anhydrous liquid ammonia,or in the form of easily decomposable organic nitrogen bases such asaliphatic amines, e.g., butyl amine, isopropyl amine, etc. Further, itmay be added either to the hydrofiner feed as illustrated, or it may beadded to the hydroner eiuent in line 31.

In preheaters 30 and 32, the inlet temperature of the respective feedmixtures is raised gradually, e.g., about 10 to 50 F. per hour, startingat about 300 F. This operation is preferably continued until bedtemperatures in hydrofiner 2 and hydrocracker 6 reach levels somewherein the range of about 40G-500 F. Before this point is reached however,it will normally be found that the wash water Withdrawn via line 34 fromhigh-pressure separator 36 will contain substantial amounts of ammonia,indicating that both the hydroning catalyst and the hydrocrackingcatalyst have become substantially saturated with adsorbed ammonia. Careshould be taken not to allow the hydrocracking catalyst temperature torise above about 500 F. until there has been a substantial breakthroughof ammonia as indicated by its appearance in the wash water from line34.

In the schedule illustrated in FIGURE 2, an inlet ternperature of about450 F. is reached in each reactor after about 6 hours, as indicated ontemperature curve A. At this point, substantial amounts of ammonia beginto appear in the wash water from line 34, and hence the amount ofammonia injected via line 20 is reduced from the original 0.5% by weightto about 0.2%, as indicated by ammonia injection profile line B. Afterreducing the arnmonia concentration it may be desirable to operate for ashort period without further temperature rise in order to be sure vthatthe lower ammonia concentration does not bring about undesirableexothermic temperature rises in reactor 6. During the entire startupprocedure, it is preferable that none of the catalyst bed temperaturesin reactor 6 be allowed to rise more than about 30 F. above the reactorinlet temperature. This may be controlled to some extent by means ofcool quench hydrogen injected via lines 38 and 40.

Ammonia injection at the lower level of about 0.2% is then continued,while again raising the reactor inlet temperatures about 10-50" F.perhour, until the desired ini tial hydrocracking and hydrofiningtemperatures, e.g., about 600-700 F., are reached. At this point, theflow of high-nitrogen process feed may be initiated by opening valve 22inline 24. Ammonia injection is preferably continued for a s-hort timeafter the start of the high-nitrogen process feed, but may if desired beterminated substantially simultaneously with the use of high-nitrogenfeed. It is entirely feasible to terminate completely the use of thelow-nitrogen startup feed as soon as operative catalyst bed temperatureshave been reached. However, in the modification illustrated in FIGURE 2,the termination of startup feed and the substitution of process feedproceeds stepwise over a period of several hours in order to avoid anyunexpected upset in process conditions, and provide a smoothertransition from 100% startup feed to 100% process feed. Thus, overfour-hour intervals, the startup feed is reduced from 100% to 70%, to50%, to 25%, to 0, while process feed is increased from 0 to 30%, to50%, to 75%, to 100%, as illustrated by lines C and D respectively.Ammonia injection is terminated about 4 hours after the shift to 30%process feed.

It will be understood that during the startup cycle, the effluent fromhydrocracker 4 is withdrawn via line 42, condensed in condenser 44, andtransferred via line 46 to high-pressure separator 36. Wash water isinjected into line 46 via line 48. The hydrogen recovered inhighpressure separator 36 is then recycled to the process via line 28,with makeup hydrogen and hydrogen sulfide being added via line 50. Thehigh-pressure condensate in separator 36 is flashed via line 52 intolow-pressure separator 54, from which light hydrocarbon gases areexhausted via line 56. Low-pressure condensate in separator 54 is thentransferred via line 58 to fractionating column 60, for the recovery ofbutanes via overhead line 62, gasoline-boilingrange material fromsidecut line 64, and gas oil as bottoms via line 66. During the startupcycle, the gas oil in line 66 may be recycled directly to line 26, or inanother modification, the entire low-pressure condensate in separator 54may be recycled back to the hydroiiner, thus bypassing fractionatingcolumn 60. Ordinarily, however it is preferred tg; fractionate thestartup efluent to recover any gasoline synthesized in hydrocracker 4.

With hydrotner 2 and hydrocracker 4 now on-stream with high-nitrogenprocess feed, operative process conditions fall within the followinggeneral ranges:

TABLE 2 Hydroiiuing Conditions Operative Preferred Temperature, F. (av.bed):

Beginning oi run 650-750 680-725 End of run 700-850 Z50-800 Pressure,p.s.i.g 300-5, 000 500-2, 500 LHSV 0. 1-20 0. 2-5 Hz/oil ratio, Ms.c.f.fb 1-25 2-15 Hydroeraeking Conditions Operative PreferredTemperature, F. (av. bed):

Beginning of run 650-775 S80-725 End of run 700-850 770-825 Pressure,p.s.i.g 30G-5, 000 500-2, 500 LHSVg 0. l-20 0. 5-5 Hr/oil ratio, Ms.c.f./b 1-25 2-15 nickel plus molybdenum, or nickel plus tungsten,preferably supported on a carrier such as alumina, or alumina containinga small amount of coprecipitated silica gel.

The hydrocracking catalysts employed herein may consist of any desiredcombination of a refractory cracking base wit-h a suitable hydrogenatingcomponent. Suitable cracking bases include for example mixtures of twoor more difcultly reducible oxides such as silica-alumina,silica-magnesia, silica-zirconia, alumina-boria, silicatitania,silica-zircona-titania, acid-treated clays and the like. Acidic metalphosphates such as aluminum phosphate may also be used. The preferredcracking bases comprise partially dehydrated, zeolitic, crystallinemolecular sieves, eg., of the X or Y crystal types, having relativelyuniform pore diameters of about 8-14 A., and comprising silica, aluminaand one or more exchangeable zeolitic cations.

A particularly active and useful class of molecular sieve crackinglbases are those having a relatively high SiO2/Al203 ratio, eg., betweenabout 3.0 and l0. The most active forms are those wherein theexchangeable zeolitic cations are hydrogen and/or -a divalent metal suchas magnesium, calcium or zinc. In particular, the Y molecular sieves,having crystal pores of about 9-10 A. in diameter, yand wherein theSiOZ/AlgOs ratio is labout 4-6 are preferred, either in their hydrogenform, a divalent metal form, or a mixed divalent metal-hydrogen form.Normally, such molecular sieves are prepared rst in the sodium form, andthe sodium is ion-exchanged out with a divalent metal, or Where thehydrogen form is desired, with an lammonium salt followed by heating todecompose the zeolitic ammonium ion and leave a hydrogen ion. (Thesehydrogen zeolites are sometimes referred to as being decationized.)Molecular sieves of this nature are described imore particularly inBelgian Patents Nos. 577,642, 598,582, 598,683 and 598,682.

The foregoing cracking bases are compounded, as by impregnation, withfrom about 0.5% to 25% ('based on free metal) of a Group VIB and/ orGroup VIII metal promoter, eg., an oxide or sulfide of chromium,tungsten, cobalt, nickel, or the -corresponding free metals, or anycombination thereof. Alternatively, even smaller proportions, betweenabout 0.05% and 2% of the metals platinum, palladium, rhodium or iridiummay be employed. The oxides and Isulfides of other transitional metalsmay also be use-d, but to less advantage than the foregoing.

In the case of zeolitic type cracking bases, it is desirable to depositthe hydrogenating metal thereon by ion exchange. This can belaccomplished by digesting the zeolite with an aqueous solution of -asuit-able compound of the desired metal, wherein the metal is present ina cationic form, and then reducing to form the free metal, as described-for example in Belgian P-atent No. 598,686.

Although as indicated afbove, substantially any hydrocrackin-g catalystmay be used herein, it is not to be assu-med that -all such catalystsare equivalent, or that they will -all give a commercially feasibleprocess. For hydrocracking at below about 825 F. as required herein, andin the presence of ammonia, it is highly desirable to use catalystswhich have both a high `cracking activity and high hydrogenatingactivity; otherwise it will be necessary to employ uneconomical lowspace velocities. For economical processes operated at above about 0.5LHSV, the preferred catalysts are composed of a Group VIII noble metal,e.g., platinum, palladium, rhodium, iridium or ruthenium, combined ybyion exchange with one of the zeolitic molecular sieve cracking bases ofthe Y crystal type, wherein the zeolitic cations are predominantlyhydrogen and/ or a divalent metal such as calcium, magnesium, or zinc.The more conventional catalysts such as platinum on silica-alumina gel,or nickel on silica-alumina gel, will require llow space velocities, ingeneral below about 0.5

.in order to achieve the desired conversion at the specifiedhydrocracking temperatures.

The following example is cited to illustrate the invention, but is notto be construed as limiting in scope:

Example This example demonstrates the superior activity of ahydrocracking catalyst preheated to hydrocracking temperatures with ahydroner effluent derived from the hydrofining of va substantiallynitrogen-free startup feed to which ammonia had been added in the formof t-butylamine. The startup feedstock was a light gas oil lboilingbetween about 420 and 520 F., containing about 2.6 parts per million ofnitrogen, 12 parts per million sulfur, and 24 Volume-percent aromatics.The high-nitrogen process feed was a heavy coker distillate gas oilboiling over the range of about 40G-875 F., having an API gravity of24.6, and cont-aining 0-.237 weightpercent nitrogen and 0.77weight-percent sulfur. The hydroning catalyst was a presulfidedcomposite of about 3% cobalt oxide and 15% molybdenum oxide supported onan alumina carrier which was stabilized `by the addition of 5% SiO2. Thehydrocracking catalyst was composed of labout 0.5% by weight ofpalladium added by ion exchange to a mixed magnesium-hydrogen zeolite ofthe Y crystal type, containing Iabout 3 weight-percent MgO.

(35% of total zeolitic exchange capacity), and having a silica/ aluminamole-ratio of about 4.7. Conditions which were substantially constantthroughout the startup in both the hydroning and the hydrocrackingreactor, were: Pressure 1,500 p.s.i.g., hydrogen-to-oil ratios about`6,000- 8,000 s.c.f./b. of feed. Liquid hourly space velocities wereabout 0.8 in the hydroner and 1.5 in the hydrocracker.

The Ihydrocracking catalyst was first brought up to about 400 F. duringan activation cycle with circulating hydrogen, and was then preheated toabout 650 F. by circulating the hot hydrofiner eiuent therethrough,containing 0.5 weight-percent nitrogen as ammonia during the first 16-hours and 0.2 weight-percent during the last 6 hours, after which theflow of startup feed was terminated, and 100% process feed was used. Toreach the desired conversion per pass of 40% by volume to 400 F.end-point gasoline, it was found that -an initial temperature of about705 F. was required, which increased after 12 days of operation to about711 F.

In an analogous startup procedure as described in Example I of SerialNo. 265,648, wherein the hydrocracking catalyst was preheated with lahydrofiner effluent derived from the hydroning of various blends ofnitrogencontaining process feed `and nitrogen-free startup feed, theinitial hydrocracking temperature required for 40% conversion was 713F., `which increased to about 719 F. after days onstream. Thus, thestartup procedure of this invention yields a catalyst having about a 7-8F. temperature advantage over the catalyst placed onstream by thestartup procedure described in Serial No. 265,648.

Results analogous to those described in the foregoing example areobtained when other feedstocks, other catalysts and other hydrocrackingconditions 4within the purview of the lbroad disclosure are substitutedin the said example. It is not intended that the invention should belimited to the details described herein, since many variations may bemade by those skilled in the art without departing from the scope orspirit of the following claims.

We claim:

1. In an integral catalytic hydrofining-hydrocracking system wherein ahydrocarbon process feedstock contaminated with organic nitrogencompounds is hydroned with added hydrogen over a bed of hydroningcatalyst at temperatures between about 650 and 850 F., and wherein thetotal effluent from said hydroining is then hydrocracked over a bed ofhydrocracking catalyst at temperatures between about 650 and 850 F., theimproved method for estab-lishing said system and raising thetemperature of said catalyst beds from initial temperatures below about500F. -to the desired Vhydroning and hydrocracking temperatures withoutdamaging said hydrocracking catalyst, which comprises:

(1) establishing a startup contacting sequence wherein a feed mixture ofhydrogen and a relatively pure hydrocarbon startup feedstocksubstantially free from organic nitrogen is preheated and passed throughsaid hydrofining catalyst bed and then through said hydrocrackingcatalyst -bed While maintaining added ammonia in the feed mixture tosaid hydrocracking catalyst bed;

(2) continuing said startup contacting sequence while incrementallyraising the hydroning inlet temperature of said feed mixture, therebygradually raising the bed temperature of said hydroiining catalyst tothe desired initial hydroiining temperature for said hydrocarbon processfeedstock, and also gradually raising the bed temperature of saidhydrocracking catalyst to the desired initial hydrocracking temperature,Ibetween 650 and 775 F.; and then (3) substantially immediatelythereafter, establishing and maintaining the desired process feedcontacting sequence by substituting said process feedstock for saidstartup feedstock and simultaneously terminating said addition ofammonia.

2. A Iprocess as dened in claim 1 wherein said added ammonia is added t0the feed mixture to said hydrofining catalyst bed.

3. A process as defined in claim 1 wherein said added ammonia is addedto the effluent from said hydrofining catalyst bed.

4. A process as dened in claim 1 wherein said hydrocracking catalystcomprises a minor proportion of a Group VIII noble metal hydrogenatingcomponent combined with a cyrstalline, zeolitic molecular sieve of the6. In an integral catalytic hydroning-hydrocracking system wherein amineral oil process feedstock containing at least about 50 p.p.m. oforganic nitrogen is hydrofined with added hydrogen over a bed ofhydrofining catalyst at temperatures 'between about 650 and 850 F., andwherein the total eluent from said hydroning is then hydrocracked over a'bed of hydrocracking catalyst at temperatures between about 650 and 850F., the improved method for establishing said system and raising thetemperature of said Vcatalyst beds from initial temperatures 'belowabout 500 F. to the desired hydroning and hydrocracking temperatureswithout damaging said hydrocracking catalyst, which comprises:

( 1) establishing a startup contacting sequence wherein a feed mixtureof Yhydrogen and a relatively pure hydrocarbon startup feedstocksubstantially free from organic nitrogen is preheated and passed throughsaid hydroning catalyst bed and then through said hydrocracking catalystbed while maintaining added ammonia in the feed mixture to saidhydrocracking catalyst bed;

(2) continuing said startup contacting sequence while incrementallyraising the hydrofining inlet temperat-ure of said feed mixture, therebygradually raising the bed temperature of said `hydrofining catalyst tothe desired initial hydroning temperature for said process feedstock,and also gradually raising the bed temperature of said hydrocrackingcatalyst to the desired initial hydrocracking temperature, between about650 and 775 F.;

(3) controlling the rate at which the temperature of said hydrocrackingcatalyst bed is raised in step 2) so as to maintain bed temperaturesbelow about 500 F. until after said hydrocracking catalyst bed issubstantially saturated with adsorbed ammonia as indicated 'by theappearance of ammonia in the eiuent therefrom;

(4) substantially immediately upon reaching hydrocracking temperaturesas recited in step (2), establishing an interim contacting sequencewherein the ow of said startup feedstock is incrementally reduced andreplaced incrementally with said process feedstock While terminating theaddition of ammonia and (5) establishing and maintaining the desiredprocess feed contacting sequence by terminating the flow of said startupfeed and continuing the ow of process feed in the absence of addedammonia.

7. A process as dened in claim 6 wherein said added ammonia is added tothe feed mixture to said hydroning catalyst bed.

8. A process as defined in claim 6 wherein said added 10 ammonia isadded to the eluent from said hydroning catalyst bed.

9. A process as dened in claim 6 wherein said hydrocracking catalystcomprises va, minor proportion of a Group VIII noble metal hydrogenatingcomponent combined with a crystalline, zeolitic molecular sieve of the Ycrystal ltype wherein the Zeolitic cations are selected mainly from theclass consisting of hydrogen and diValent metals.

References Cited by the Examiner UNITED STATES PATENTS 6/1965 Wood208-254 10/1965 Arey 208-111

1. IN AN INTEGRAL CATALYTIC HYDROFINING-HYDROCRACKING SYSTEM WHEREIN AHYDROCARBON PROCESS FEEDSTOCK CONTAMINATED WITH ORGANIC NITROGENCOMPOUNDS IS HYDROFINED WITH ADDED HYDROGEN OVER A BED OF HYDROFININGCATALYST AT TEMPERATURES BETWEEN ABOUT 650* AND 850*F., AND WHEREIN THETOTAL EFFLUENT FROM SAID HYDROFINING IS THEN HYDROCRACKED OVER A BED OFHYDROCRACKING CATALYST AT TEMPERATURES BETWEEN ABOUT 650* AND 850*F.,THE IMPROVED METHOD FOR ESTABLISHING SAID SYSTEM AND RAISING THETEMPERATURE OF SAID CATALYST BEDS FROM INITIAL TEMPERATURES BELOW ABOUT500*F. TO THE DESIRED HYDROFINING AND HYDROCRACKING TEMPERATURES WITHOUTDAMAGING SAID HYDROCRACKING CATALYST, WHICH COMPRISES: (1) ESTABLISHINGA STARTUP CONTACTING SEQUENCE WHEREIN A FEED MIXTURE OF HYDROCARBON ANDA RELATIVELY PURE HYDROCARBON STARTUP FEEDSTOCK SUBSTANTIALLY FREE FROMORGANIC NITROGEN IS PREHEATED AND PASSED THROUGH SAID HYDROFININGCATALYST BED AND THEN THROUGH SAID HYDROCRACKING CATALYST BED WHILEMAINTAINING ADDED AMMONIA IN THE FEED MIXTURE TO SAID HYDROCRACKINGCATALYST BED; (2) CONTINUING SAID STARTUP CONTACTING SEQUENCE WHILEINCREMENTALLY RAISING THE HYDROFINING INLET TEMPERATURE OF SAID FEEDMIXTURE, THEREBY GRADUALLY RAISING THE BED TEMPERATURE OF SAIDHYDROFINING CATALYST TO THE DESIRED INITIAL HYDROFINING TEMPERATURE FORSAID HYDROCARBON PROCESS FEEDSTOCK, AND ALSO GRADUALLY RAISING THE BEDTEMPERATURE OF SAID HYDROCRACKING CATALYST TO THE DESIRED INITIALHYDROCRACKING TEMPERATURE, BETWEEN 650* AND 775*F.; AND THEN (3)SUBSTANTIALLY IMMEDIATELY THEREAFTER, ESTABLISHING AND MAINTAINING THEDESIRED PROCESS FEED CONTACTING SEQUENCE BY SUBSTITUTING SAID PROCESSFEEDSTOCK FOR SAID STARTUP FEEDSTOCK AND SIMULTANEOUSLY TERMINATING SAIDADDITION OF AMMONIA.